Hydraulic couplings have previously utilized hydraulic pumps to couple rotary members of a vehicle drivetrain. For example, U.S. Pat. No. 4,012,968 Kelbel discloses a differential mechanism wherein a hydraulic pump of the Gerotor type is located radially outward from the axis of rotation of the two members and provides pumped hydraulic fluid to a clutch that controls operation of a bevel type planetary gear set to limit the differential action so as to thus have a limited slip function. U.S. Pat. No. 4,730,514 Shikata et al. discloses another differential mechanism wherein a hydraulic pump controls operation of a bevel gear type planetary gear set that extends between two rotary members such that a limited slip function of the differential gear operation is also provided. Furthermore, U.S. Pat. Nos. 4,719,998 Hiramatsu et al.; 4,727,966 Hiramatsu et al. and 4,909,371 Okamoto et al. disclose hydraulic pumps utilized within vehicle drivetrains to control actuation of a clutch that connects two rotary members of a vehicle drivetrain.